During the course of dental treatment, dental files are inserted into the root canal to remove nerve and blood vessels. A major concern is to locate the apical constriction (minor foramen) for determining the working length and/or the apex (major foramen) to avoid surpassing the apex into the soft tissue.
Towards this end, a probe or electrode is typically inserted into the root canal, and the location of the apical region of the tooth is detected by measuring the resistance or the impedance between the inserted electrode and a second external electrode located outside of the tooth, usually connected to oral soft tissue. Thus, as the leading edge of the root canal probe or electrode approaches the apical position, the resistance or impedance between the root canal electrode and the external electrode changes. The resistance or impedance value is correlated with the depth of the probe tip in the root canal, allowing the dental practitioner to detect the apical position of the tooth. Typically, the apex locator instrument includes a display panel, which indicates the distance between a fixed point on the probe (e.g. the probe tip) and a fix point in the apical region (e.g. the apex, or a location of the apical constriction).
To date, apex locator instruments suffer from a number of shortcomings. For example, in many clinical situations, the value displayed by the apex instrument is not stable, making it difficult for the practitioner to determine the distance between the tip of the probe and the apex or apical constriction. Another source of inaccuracy stems from the fact that root canal dimensions and physical properties vary between specific teeth and patients, and thus many devices provide accurate readings for certain patients and erroneous readings for others.
Another source of inaccuracy stems from the fact that changes in an amplitude of current through biological tissue between the root canal and another location in the body may change the electrical properties of this biological tissue, introducing inaccuracies in a computed distance between the probe and the apical region.
Thus, there is an ongoing need for improved methods and apparatus for determining the position of a probe or electrode inserted within the root canal of a tooth.
Below is a listing of patents, published patent applications, and non-patent publications that provide potentially relevant related art. Each patent, published patent application, and non-patent publication is incorporated herein by reference in its entirety.
U.S. Pat. No. 4,272,531; U.S. Pat. No. 3,993,044; U.S. Pat. No. 4,447,206; U.S. Pat. No. 4,243,388; U.S. Pat. No. 3,901,216; U.S. Pat. No. 3,753,434; U.S. Pat. No. 5,096,419; U.S. Pat. No. 5,112,224; U.S. Pat. No. 5,211,556; U.S. Pat. No. 5,295,833 and U.S. Pat. No. 6,221,031.